In drilling oil and gas wells, after a productive hydrocarbon zone has been reached it is often necessary to run a well casing into the wellbore. The casing is then anchored into place by injecting a volume of cement into the annulus between the wellbore wall and the casing. The cement anchors the casing into place and seals the hydrocarbon zone to prevent the migration of fluids from one zone to another through the annular space. Unfortunately, the casing blocks the flow of formation fluid, in particular hydrocarbons, into the interior of the casing.
In order to produce the hydrocarbons from a wellbore, it is necessary to provide a series of lateral perforations through the casing and any adjacent cement. In many instance a perforation gun is used to perforate the casing and the adjacent cement.
A perforation gun may use a series of shaped charges to perforate the casing. The perforation gun is lowered into the vicinity of the casing that is desired to be perforated and, upon actuation of the perforation gun from the surface, the shaped charge is fired, penetrating the casing and adjacent cement. After the casing has been perforated approximately adjacent to a hydrocarbon producing formation the formation is typically fractured or otherwise treated to enhance the production of hydrocarbons from the zone.
Presently it is becoming more common to drill through multiple zones with a single wellbore and due to the structure of the formation zones long horizontal sections are increasingly becoming the typical method of drilling a well. As horizontal completions become increasingly common, it is desirable, due to the high cost of standby time for the fracturing and well treating equipment, to minimize the time required to set up and complete the treatment or fracturing of one hydrocarbon producing zone and move to the next hydrocarbon producing zone in the same wellbore.
One method of decreasing the high cost of standby time for the fracturing and well treating equipment, that has been developed is to incorporate sliding sleeves with ball valves into the casing string and then to cement the tubular in place including the sliding sleeves. With sliding sleeves cemented into place a perforating gun is not necessary as ports are provided in the sliding sleeves. When it becomes necessary to open a sliding sleeve a ball or other plug is circulated downhole to open the sleeve allowing the operator to fracture or treat the desired hydrocarbon producing zone.
The drawback to such a system is that the decision to complete the well with sliding sleeves must be made relatively early, a complete system must be purchased, and the complete system should be precisely incorporated into the tubular assembly to correspond with each hydrocarbon producing zone.